Japanese Patent Laying-Open No. 10-270804 discloses a nitride semiconductor light emitting device having a light emitting layer including GaNAs (or GaNP or GaNSb) quantum well layers and GaN barrier layers. Further, Japanese Patent Laying-Open No. 11-204880 discloses a nitride semiconductor light emitting device having a light emitting layer including InGaNAs well layers and GaN barrier layers and emitting light of a wavelength of more than 450 nm.
However, the inventors have found that, with these nitride semiconductor light emitting devices of the prior art, it is difficult to improve steepness in composition change at the interface (hereinafter, referred to as “interfacial steepness”) between the well and barrier layers included in the light emitting layer even if their growth conditions (including growth temperature) are controlled. Insufficient interfacial steepness between the well and barrier layers causes increase of half-width of emission peak, increase of color mottling, and degradation of luminous intensity (or gain reduction) in the light emitting device. Further, the fact that it is difficult to improve the interfacial steepness between the well and barrier layers means that it is difficult to form a multiple quantum well structure including a plurality of well and barrier layers. Such problems are commonly seen in nitride semiconductor light emitting devices having light emitting layers including GaNAs well layers/GaN barrier layers, GaNP well layers/GaN barrier layers, GaNSb well layers/GaN barrier layers, InGaNAs well layers/GaN barrier layers, InGaNP well layers/GaN barrier layers, InGaNSb well layers/GaN barrier layers and others.